Mozilla has created a browser extension to let you log onto web sites from your browser tool bar. You can get the Sign-In Add-On here.

My take: The idea as described does not go far enough. What's needed: encryption of all the log-in information and the requirement to log into that cache of user ids and passwords every time you start up the browser. Ideally it should be possible to move that encrypted file between PCs and not worry if, say, the USB memory stick you use to move it gets stolen.

The problem as I see it is that at least some of us have far too many online accounts to places where we would not want anyone else to get access. Lots of online store accounts, bank accounts, brokerage accounts, and other accounts are basically keys to the ability to spend money and transfer money. These accounts need to be hard to get to. The information about them should be encrypted and logging into a PC should not by itself enable someone to get into that information. We need to move files between PCs and servers anyway. So there are other points of vulnerability.

Even an unlockable encrypted file doesn't seem like enough security. A browser can be hacked and browser makers do frequent releases of security hole patches. If a browser can get into your account information then so potentially could a hacker. So we need more layers of security. Though I'm not sure what those other layers should be.